A shell-and-tube flooded type evaporator has a shell; the shell has a bottom and defines a space. A group of tubes are arranged near the bottom of the shell of the evaporator and extend horizontally from one end of the shell to the other end. The group of tubes is used to carry process fluid which passes through the shell from a process fluid inlet to a process fluid outlet. Refrigerant, as the working fluid, enters the shell of the evaporator from a refrigerant inlet, for example, near the bottom of the shell, exchanges heat with the process fluid and is vaporized. The refrigerant vapor enters an upper portion of the space in the shell and leaves the shell via a refrigerant outlet which can be positioned at an upper portion of the space in the shell.
In the shell-and-tube flooded type evaporator, the number of tubes, the material, length, and performance characteristics of the tubes are carefully chosen to provide the proper heat transfer as well as to reduce cost, reduce the process fluid pressure drop, and reduce the amount of refrigerant charge. In a two-pass shell-and-tube flooded type evaporator, a typical configuration of the tubes has process fluid flowing first in a direction away from the process fluid inlet and then in a direction back toward the process fluid inlet to flow through the outlet. This arrangement places both the process fluid inlet and the process fluid outlet at the same end of the shell of the evaporator.
The size of the shell of the evaporator typically is set large enough to accommodate the tubes so that refrigerant vapor exiting at the top of the shell does not have undesired interactions such as liquid carry-over, heat exchange imbalance, and/or certain local flow velocities with the process fluid flowing in the tubes near the bottom of the shell. The size of the evaporator may also be set by other features of the chiller, for instance the compressor. Various loads for the compressor may require different sizes of the evaporator shell.